The Hermit Hacker wrote:
>
> > What I would ask from you?
> > 1) First of all, if my needs could be satisfied in other way with
> > current functions in libpq of libpgtcl. I can assure you that with
> > current libpgtcl is rather impossible. I am not sure if there is another
> > mechanism using some subtle functions that I didn't know about them.
>
> Bruce answered this one by asking about cursors...
Yes. It's true. I have used cursors for speeding up opening tables in
PgAccess fetching only the first 200 records from the table.
But for a 10 thousand record table I will send over the network 10
thousand "FETCH 1 IN CURSOR" because in a report table I am processing
records one by one.
The time for this kind of retrieval would be more than twice as in the
'callback' mechanism.
If you think that is better to keep libpq and libpgtcl as they are, then
I will use cursors.
But using the 'callback' method it would increase performance.
I am waiting for the final resolution :-)
> Basically, by "cloning", you are effectively looking at implementing ftp's
> way of dealing with a connection, having one "control" channel, and one "data"
> channel, is this right? So that the "frontend" has a means of sending a STOP
> command to the backend even while the backend is still sending the frontend
> the data?
Not exactly. Looking from Tcl/Tk point of view, the mechanism is
transparent. I am using this structure :
pg_loop $database "select * from sometable" record {
set something $record(somefield)
}
But the new libpgtcl is opening a 'cloned' connection in order to :
- send the query through it
- receive the data from it
I am not able to break the connection using commands send through the
'original' one. The query is 'stopped' by breaking the connection.
That's why we needed another connection. Because there isn't (yet) a
mechanism to tell the backend to abort transmission of the rest of the
query. I understand that the backend is not reading any more the socket
in order to receive some CANCEL signal from the frontend. So, dropping
the rest of the query results isn't possible without a hard break of the
connection.
--
Constantin Teodorescu
FLEX Consulting Braila, ROMANIA